<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title></title>
	<style>
		#dv {
			width: 400px;
			height: 300px;
			border: 1px solid red;
		}
	</style>
	<script src="itcast 2.js"></script>
</head>
<body>
	<div id="dv"></div>
</body>
<script>
	I( '#dv' ).hover( function () {
		this.style.backgroundColor = 'pink';
	}, function () {
		this.style.backgroundColor = '';
	});

</script>
</html>